Electroplating is an electrochemical process in which current flow through an electrolytic solution from a positively charged electrode (anode) to a work-piece deposits a thin layer or plating of metal thereon. A conventional fountain-type electroplating apparatus for plating planar work-pieces, such as semiconductor substrates, is shown schematically in FIG. 1. Referring to FIG. 1, an apparatus 100 generally includes an inner plating tank or cup 102 containing an electrolytic solution (the motion of which is indicated by the arrows), an electrolyte inlet 104 and an electroplating power supply 108. Electroplating power supply 108 is electrically coupled to an anode 110 in plating tank 102 and, via conductive supports 112, to a work-piece or substrate 114 supported above plating tank 102. Apparatus 100 may be positioned above an overflow tray for catching effluent from plating tank 102, and further above an electrolyte recirculation system or pump (not shown).
In operation, a positive charge is applied to anode 110 and a negative charge is applied to substrate 114, which serves as the cathode, through conducting supports 112. As the electrolytic solution is circulated past anode 110 toward substrate 114 by a recirculation pump, metal ions dissolved in the solution plate out on substrate 114. The source of the material to be deposited (metal ions) may be a consumable anode 110, or a non-consumable anode with a source attached thereto. Generally, when a non-consumable anode is used the metal ions come from an external source, such as an anode bag attached to the anode. In fountain plating, if a non-consumable anode is used, the anode bag may rest on the non-consumable anode.
While the above-described fountain-type electroplating apparatus provides a relatively rapid and economical approach to providing substantially uniform plating on a surface of semiconductor substrate, it does have a number of disadvantages or drawbacks. One potential drawback associated with conventional electroplating apparatuses and methods is the generally undesirable plating that occurs on a radial side or edge 116 of substrate 114 and which can, under certain circumstances, even extend to a top surface 118 thereof. Past attempts to eliminate this undesirable edge coat have focused on the use of a thick or extensive edge protection coating formed on the edge or top surface of the substrate prior to electroplating. These solutions have also not been wholly satisfactory for a number of reasons. In particular, the additional processing operations needed to deposit, pattern, develop and then strip the edge coating material, such as a photo-resist edge coating material, after electroplating can add significantly to the fabrication cost or time.